How to download the image
Right click and select "Save image".
How to change the background on Windows
To change the desktop background. Open Desktop Background by clicking the Start button , clicking Control Panel, clicking Appearance and Personalization, clicking Personalization, and then clicking Desktop Background. Click the downloaded image.
How to change the background on a Mac
To do this, click the Apple menu on the panel at the top of your screen, click System Preferences, and click Desktop and Screensaver. Choose a new wallpaper and it will appear only on the current desktop. If you'd like to change the wallpaper for another desktop, move the window to another desktop and change it again.